Calipers



UNITED STATES PATENT OFFICE.

JOHN BYSTROM, OF CHICAGO, ILLINOIS.

CALIPERS.

SPECIFICATION forming part of Letters Patent No. 579,951, dated April 6, 1897.

7 Application filed September 23,1895. Serial No, 563,359. (No model.)

To all whom it may concern.-

Be it known that 1, JOHN BYSTROM, a citizen of the United States, residing at Chicago, county of Cook, State of Illinois, have invented a certain new and useful Improvement in Calipers and I declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it pertains to make and use the same, reference being had to the accompanying drawings, which form a part of this specification, in which Figure l is a plan view of the instrument, the legs slightly opened, having the outer plate of one of the legs broken away so as to show the testing-finger; Fig. 2, a sectional view on line 2 2 of Fig. 1; Fig. 3, a view of the inside calipers constructed by my improved method; Fig. 4, a plan section on line 4 4 of Fig. 3.

My invention relates to an improvement in the construction of mathematical instruments, especially that of the caliper; and the objects of this invention are to construct the instruments by building them up of several thicknesses of thin metal material, thus making them cheaper and at the same time have them of greater stiffness than those now in use; to so construct them that the points of the legs will be in the same line, and to provide the ordinary or outside calipers with a spring testing-finger so adapted that the difference of one one-thousandth of an inch either larger or smaller than the measurement desired, and to which it has been previously set, can be readily ascertained. By this method of construction there is much less work required than by the old method, as the center piece of one leg fits between the outer plates of the other leg, thus making the joint without the expensive work of millingand slotting that' is required when the legs are made of single pieces. I attain these objects in a manner hereinafter described and claimed.

In the drawings, A represents the caliper, A being the legs thereof, and A the swivel; A the points at which the measurement is taken.

As will be seen by reference to Figs. 2 and 4, the instruments shown are made of three pieces riveted together.

B represents the guide and lock bar, it being an extension of the center plate and provided with a slot 1).

B is a set-screw which passes through one of the outer plates, through the slot 6, and, by means of male and female screw-thread, is adapted to enter the plate on the opposite side, locking the jaws in any position when tightened.

The center plate on one of the jaws A, Fig. l, is cut away to accommodate the spring 0 and the finger D. The spring is made a trifle less in thickness than the center plate and is fastened in place by rivets or similar devices. The finger D is also a trifle less in thickness than the center plate and is pivoted between the outer plates and in the space left by cutting away the center plate at or near the point of the leg which comes in contact with the article measured by pivot c, the end 0 belowthe pivot 0 being allowed to project slightly beyond the point of the leg proper. The opposite end 0 turns about at right angles to the main portion of the spring D and passes out through an opening d, made by cutting away the center plate, and slides on the surface of an outwardly-extending projection d,

formed by a portion of each plate used in the construction projecting beyond the line of the leg of the caliper. The upper side of the projection d and the under side of the end 0 of the finger D are made circular, of a radius equal to the distance from pivot c. The projection d also has upon its upper surface marks or graduations indicating the movement of one one-thousandth of an inch of the end 0 of the finger D, but of course would be.

farther apart than one one-thousandth of an inch-as, for example, suppose the distance from the pivot C to the end 0 to be twenty times greater than the distance from c to the end 0 the marks or graduations above mentioned would be one-twentieth of one thousand or one-fiftieth of an inch apart. These graduations are made above and below a central line or mark for the purpose of determining whether the piece examined is larger or smaller than the measurement at which the instrument has previously been set.

E is a small set-screw for the purpose of setting the finger D when desired at a predetermined point.

The use and operation of the instrument are as follows, viz: Suppose it is desired to turn a piece of metal down to three-quarters of an inch in diameter and to have it measure exact or at least to one one-thousandth of an inch of the desired diameter. The finger D is set, by means of the set-screw E, so that the pointer end 0 registers exactly to the center line or graduation 011 the projection d above mentioned. The set-screw B is then loosened and the legs of the instrument set, with the use of an ordinary scale, so that the points A are three-fourths of an inch apart. The work is then turned down to approximately three-fourths of an inch, when the set-screw E is withdrawn, allowing the free movement of the finger D. The instrument is then passed over the work, and the pressure against the end 0 of the finger D will cause said finger to indicate on the marked surface of the projection d whether the piece is too large or too small in diameter, for if the pointer 0 remains below the central mark it will indicate that the work is too small, and if it registers above said center line it indicates that the work is too large in diameter.

It will be seen from the above description that this device is especially convenient for those having the overseeing and inspecting of the work in any machine-shop, as every piece may be readily tested for its accuracy.

Having thus described my invention, what I claim isl. The combination with a caliper having two legs and provided with means for locking the legs thereof in any position, of a springfinger pivoted near its end to a predetermined point near the point of contact of one of said legs, in a manner allowing the end of said finger below said pivot to come in contact with the article measured, the opposite end terminating upon a graduated surface, said surface having graduations above and below a center line, said second end of said finger bearing a predetermined proportion to the said first-mentioned end, said finger being for the purpose of indicating a small fraction of an inch when taking a measurement, and means for setting said finger at the said center mark, substantially as described.

2. A mathematical instrument constructed of three pieces of sheet metal riveted or 0therwise secured together, the center plate of one leg adapted to enter between the outside plates of the other leg for the purpose of a joint or hinge, and for the further purposes of bringing the points of the legs in a direct line with one another and to stand a greater resistance to twisting'strain, substantially as described.

3. A caliper having two rigid legs pivoted together at one end, one of said legs being partially hollow and having a projection on its outer side, said projection having a graduated surface on its upper edge; a finger contained in said hollow and pivoted at a point near its lower end near the point of contact of said hollow leg, and projecting beyond the end thereof; the upper end of said finger bearing a predetermined proportion to said lower end and terminating on said graduated surface of said leg substantially as and for the purposes set forth.

4. A caliper having two rigid legs pivoted together at one end, one end of said legs being provided with a finger pivoted at a predetermined point near the point of contact of said leg and having one end projecting beyond the lower point of said leg, the opposite end terminating upon a graduated surface formed on said leg, said graduations being formed by one central line or mark and one or more lines or marks on either side thereof substantially as and for the purposes set forth.

In testimony whereof I sign this specification in the presence of two witnesses.

JOHN BYSTROM.

Witnesses:

CLIFFORD N. WHITE, E. H. XVHITE. 

